Residual lignin inhibits thermal degradation of cellulosic fiber sheets

The market for cellulosic fiber based food packaging applications is growing together with the importance of improving the thermal durability of these fibers. To shed light on this, we investigated the role of residual lignin in pulp on the thermal stability of refined pulp sheets. The unbleached, oxygen delignified, and fully bleached pulp sheets were studied after four separate refining degrees. Comparison by Gurley air resistance, Bendtsen porosity, and the oxygen transmission rate tests showed that lignin containing sheets had better air and oxygen barrier properties than fully bleached sheets. Sheet density and light scattering coefficient measurements further confirmed that the lignin containing pulps underwent more intense fibrillation upon refining that changed the barrier properties of the sheets. Thermal treatments (at 225 °C, 20 and 60 min, in water vapor atmospheres of 1 and 75 v/v %) were applied to determine the thermal durability of the sheets. The results revealed that the residual lignin in pulps improved the thermal stability of the pulp sheets in the hot humid conditions. This effect was systematically studied by tensile strength, brightness, and light absorption coefficient measurements. The intrinsic viscosity results support the findings and suggest that lignin is able to hinder the thermal degradation of pulp polysaccharides. In spite of the fact that lignin is known to enhance the thermal yellowing of paper, no significant discoloration of the pulp sheets containing residual lignin was observed in the hot humid conditions (75 v/v %). Our results support the idea of lignin strengthening the thermal durability of paper.     

Coating of open tubular capillaries with discoidal and spherical high-density lipoprotein particles in electrochromatography

A new method was developed for the coating of fused-silica capillaries with human high-density lipoproteins (HDLs) for use in electrochromatography. The HDL particles used for the coating differed in particle shape and composition. Both discoidal and spherical particles formed a monolayer on the inner silica wall as confirmed by atomic force microscopy. The effect of coating conditions, such as HDL concentration and coating time, was investigated with spherical HDL particles. Examination of the influence of pH on the coating stability also allowed the determination of pI values for the HDL particles attached to the capillary wall. The pI values for spherical and discoidal HDL particles were close to 5.0. The repeatabilities of the EOF mobility and the retention factors of the uncharged steroid hormones used as model compounds were exploited in the evaluation of the coating stability. The optimal coating was achieved with 0.1 mg/mL HDL protein and 50 min flushing with coating solution followed by 15 min standing time. Electrochromatography with HDL-coated open tubular capillaries offers a new tool for the study of HDL particle structure and transformations.     

New bonding modes for boraamidinate ligands in heavy group 15 complexes: fluxional behavior of the 1:2 complexes, LiM[PhB(NtBu)2]2 (M = As, Sb, Bi)

The reactions of MCl3 with Li2[PhB(NtBu)2] in 1:1, 1:1.5, and 1:2 molar ratios in diethyl ether produced the monoboraamidinates ClM[PhB(NtBu)2] (1a, M = As; 1b, M = Sb; 1c, M = Bi), the novel 2:3 boraamidinate complexes [PhB(NtBu)2]M-micro-N(tBu)B(Ph)N(tBu)M[PhB(NtBu)2] (2b, M = Sb; 2c, M = Bi), and the bisboraamidinates LiM[PhB(NtBu)2]2 (3a, 3a.OEt2, M = As; 3b, M = Sb; 3c.OEt2, M = Bi), respectively. The 2:3 complexes 2b and 2c were also observed in the reactions carried out in a 1:2 molar ratio at room temperature. All complexes have been characterized by multinuclear NMR spectroscopy (1H, 7Li, 11B, and 13C) and by single-crystal X-ray structural determinations. The molecular units of the mono-boraamidinates 1a-c are isostructural, but their crystal packing is distinct as a result of stronger intermolecular close contacts going from 1a to 1c. In the novel 2:3 bam complexes 2b and 2c, each metal center is N,N'-chelated by a bam ligand and these two [M(bam)]+ units are bridged by the third [bam]2- ligand. The structures of the unsolvated bis-boraaminidate complexes 3a and 3b consist of [Li(bam)]- and [M(bam)]+ monomeric units linked by Li-N and M-N bonds to give a tricyclic structure. Solvation of the Li+ ion by diethyl ether results in a bicyclic structure composed of four-membered BN2As and six-membered BN3AsLi rings in 3a.OEt2. In contrast, the analogous bismuth complex 3c.OEt2 exhibits a tetracyclic structure. Variable-temperature NMR studies reveal that the nature of the fluxional behavior of 3a-c in solution is dependent on the group 15 center.     

Probing surface plasmons by bare V-shaped tips: modeling by geometrical optics and rigorous diffraction theory

Optical Review - We consider probing inhomogeneous waves in the near fields of metallic nanostructures with the aid of a dielectric V-shaped wedge connected to a waveguide. A geometrical model...     

Lignans from the bark extract of Pinus sylvestris L

Three lignans were isolated from a bioactive fraction of the 70% aqueous acetone extract of the pine (Pinus sylvestris L.) bark. Their structures were identified by high-resolution positive ion EI mass spectrometry and NMR spectroscopy. The complete assignment of proton and carbon signals was achieved by 2D NMR experiments: HSQC, HMBC, DQF-COSY and NOESY.     

New isomers of 4,1-benzothiazepines. The first evidence for the desmotropy of seven-membered heterocycles

A novel procedure was developed for the preparation of 2,3-disubstituted 4,1-benzothiazepines, via the ring transformation of (2R^∗,2aS^∗)-2-chloro-2a-phenyl-2,2a-dihydro-2H,4H-azeto[1,2-a][3,1]benzothiazin-1-one (1) with sodium ethoxide in ethanol. The tautomeric products (R^∗)-3-ethoxycarbonyl-2-phenyl-3,5-dihydro-4,1-benzothiazepine (4) and 3-ethoxycarbonyl-2-phenyl-1,5-dihydro-4,1-benzothiazepine (5) exhibit the rare phenomenon of desmotropy of the condensed seven-membered heterocycles. Surprisingly, these desmotropes could be separated by column chromatography. The products are unexpectedly stable in solution and their structures were proved by means of NMR and mass spectrometry.     

Synthesis and mass spectral study of new phenylsulfonyl substituted isoxazolidines

Ten 2,3‐disubstituted 4‐phenylsulfonyl isoxazolidines ( 3a‐j ) were prepared by 1,3‐dipolar cycloaddition reaction of substituted nitrones ( 1a‐j ) with phenyl vinyl sulfone ( 2 ). The reaction products were identified by means of IR, NMR, and MS data. In addition, the factors influencing on the electron ionization induced mass spectral fragmentation of the title products are discussed in detail.